Modern wireless communications devices often support signal transmission and reception over multiple frequency ranges or “bands,” using one of several distinct communications protocols or standards. For example, a single cellular phone may be required to communicate using any or all of the WCDMA, CDMA, GSM, EDGE, and LTE standards for cellular telephony, over any of several frequency bands allotted to such communications by a cellular service provider.
The radio-frequency (RF) circuitry supporting each mode and frequency band typically must satisfy different, oftentimes conflicting, design constraints. For example, in GSM, the output power requirement for the transmit circuitry is relatively high, and the out-of-band spurious emissions requirement is relatively stringent. However, the peak-to-average ratio (PAR) of a GSM signal is relatively low, so a high degree of linearity is not demanded from the transmitter circuitry. On the other hand, the PAR of a WCDMA signal is relatively high, mandating a transmitter having a high degree of linearity.
To accommodate different RF requirements of the various standards and frequency bands supported by a device, multiple transmit (TX) signal paths are often provided in the same device, each signal path designed for a specific standard/frequency band. This requires that certain component circuitry, such as TX filters and amplifiers, be replicated multiple times in a single device, leading to higher die area and higher cost. It would be desirable to have techniques for providing a wireless communications device that can flexibly operate according to multiple standards and/or frequency bands while avoiding unnecessary replication of component circuitry.